1. Field of the Invention
The invention relates to a technique for positioning carriers, which are transported by a transport conveyor, in a heating furnace.
2. Description of the Related Art
Various techniques have been suggested for positioning work or a carrier transported by a transport conveyor. For example, Japanese Utility Model Publication No. 1-15199 (JP-Y-1-15199) describes a technique for positioning first one substrate by a positioning mechanism when a plurality of substrates (work) in a transport path are transported by a comb-shaped guide member having a plurality of protrusions and then the first one substrate in the transport direction reaches a predetermined position. The positioning mechanism positions a substrate using, for example, a block equipped with a piston and rollers provided at a distal end of a cylinder for guiding a substrate.
In addition, various techniques have been suggested for checking whether positioning is accurately performed. For example, Japanese Patent Publication No. 2-49856 (JP-B-2-49856) describes a technique for checking whether there is a pallet on a swiveling table. In the technique, positioning means for positioning a pallet by fitting a movable pin in a recess formed in the pallet and detecting means for detecting whether the movable pin is fitted in the recess of the pallet are provided. In this technique, one pallet is positioned by the positioning means, and then completion of the positioning may be checked by the detecting means.
However, the techniques described in JP-Y-1-15199 and JP-B-2-49856 have the following problems. That is, according to the technique described in JP-Y-1-15199, it is not checked whether a substrate is accurately positioned after the substrate has been positioned. Therefore, if the substrate is not accurately positioned because, for example, work gets caught on something, it may be impossible to, for example, process or treat the work appropriately.
In addition, in the technique described in JP-B-2-49856, completion of positioning is checked by the detecting means; however, this technique is not directed to simultaneously positioning a plurality of pallets and then checking the positioning of the plurality of pallets, there is still a problem that working efficiency is poor.